1. Field
This invention is concerned generally with blood collection test tubes or devices which are ultimately used to separate whole blood into serum and clot portions to facilitate analysis of the blood. Specifically, the invention is concerned with an improved gel-like composition which can be used in such blood collection tubes. The composition has physical and chemical properties which, in the presence of whole blood, permit the composition to be centrifuged to a position intermediate that of the serum and clot portions and, hence, form a barrier between the two portions.
2. Prior Art
The specific gravity of whole human blood is generally within the range of about 1.048 to 1.066. It has long been known that such blood can be readily centrifuged to effect a separation of the blood into two major components-- a lighter serum portion having a specific gravity within the range of about 1.026 to 1.031 and a heavier clot portion, consisting mainly of red blood cells, having a specific gravity within the range of about 1.092 to 1.095. Such separations of whole blood into its two major components have greatly facilitated physical and chemical analyses of blood and, hence, assisted in the diagnosis and prognosis of many human ailments.
With the advent of modern sophisticated techniques for the analysis of various physical and chemical sub-components of blood, there has been a general recognition that simple centrifugation of whole blood into its two major components does not necessarily effect an ideal separation for analytical purposes. For example, even though simple centrifugation yields a gross separation of whole blood into serum and clot portions, there still exists an interface between the separated portions which, especially with time, results in the diffusion of various sub-components of one separated portion into the other. Such diffusion can affect the accuracy of various analyses.
In recent years, efforts have been made to overcome the problems associated with simple centrifugation. For example, it is now well known that various materials or devices having a specific gravity between those of the serum and clot portions can be used to assist in the separation and partitioning of the serum and clot portions. One such material consists of a gel-like, relatively inert, viscous composition having a specific gravity within the range of about 1.030 to about 1.050. Typical components of such a composition are a silicone fluid and a particulate silica filler. When whole blood, contained, for example, in a test tube, is centrifuged in the presence of such a composition, the composition, because of its specific gravity and other properties, tends to migrate to a position intermediate the serum and clot portions. Because of its thixotropic nature, the composition ultimately assumes a configuration which discourages and prevents formation of a serum-clot interface, thereby forming a physical and chemical barrier between the serum and clot portions.
Various examples of such silica-silicone fluid compositions are well known in the art and described in detail, for example, in U.S. Pat. No. 3,780,935 to Lukacs and Jacoby and U.S. Pat. No. 3,852,194 to A. R. Zine, both of which are incorporated herein by reference thereto. In the above cited patents, preferred compositions consist essentially of two components--a silicone fluid such as a dimethylpolysiloxane and very fine silica particles which act as a filler to assist in forming a gel-like material having an appropriate specific gravity. Such components have tended to be preferred because they are essentially inert and, in combination, permit control of both specific gravity and viscosity. An improved and stabilized silicone oil-silica composition is disclosed in detail in my related application Ser. No. 532,946, filed Dec. 16, 1974, entitled "Stabilized Blood Separating Composition", and assigned to the present assignee.
Although various silicone oil-silica gel-like materials have been used commercially for blood separating purposes, it can be appreciated that, because of the need for an essentially inert and relatively pure silicone oil, the cost of such gel-like materials is relatively high. Attempts have been made recently to find or develop other, preferably less expensive, fluids having essentially the same desirable properties as the silicone fluids. See, for example, my recently filed patent application cited above as a related application and which discloses the use of mineral oil as a less expensive fluid.
Quite surprisingly, I have found that there exists another relatively simple and inexpensive class of materials which is ideally suitable as one component of blood separation barriers. This discovery is rather surprising since, prior to my discovery disclosed in detail below, the materials had not been used associated with the separation of blood components although the use of hydrocarbons in general has been suggested in my earlier patent, U.S. Pat. No. 3,852,194.